Todays launch of the Falcon 9 carrying the Dragon spacecraft for the CRS-10 mission was scrubbed until tomorrow, February 19th. The reason? An issue with Thrust Vector Control (VTC for short) on the 2nd stage. Reports are early, so I don’t have details, but this seems to have been the key issue for the scrub, as announced when the abort happened 15 seconds before liftoff.
Thrust Vector Control, quite simply, is the ability for a rocket engine to deflect its thrust in such a way that the booster can be steered where it needs to point. This is usually done by moving the entire engine bell off-axis slightly, via use of a system known as a gimbal, shifting the center of thrust where it needs to be to adjust the orientation of the booster as it fires. Simple, but effective, and when done in pairs of engines, or with additional smaller control thrusters, very precise maneuvers can be conducted.
The second stage of Falcon9 uses the latter configuration, one main engine that can adjust in the X and Y axis (for basic “up, down, left right” movement, and a set of smaller thrusters to control roll and more fine adjustments as it climbs towards orbit.
Now, if TVC failed during the flight, SpaceX and NASA could easily have lost the vehicle due to a failure to be inserted into a proper orbit. Naturally, just as you need to be able to steer your car, you need to be able to steer your rocket; it’s not optional. If the Dragon was put into the wrong orbit, it might not have the fuel needed to get itself to the International Space Station to deliver its supplies, or worse, not even reach any kind of proper orbit and just fall back into the atmosphere and burn up. Neither are good outcomes, needless to say.
It looks like SpaceX will continue to look at this issue and plan for an early launch tomorrow morning. I guess I’ll have to get up early again to catch that one.